In a game of Go, Black has the advantage of first move. In order to compensate for this, White can be given an agreed, set number of points before starting the game. These points are called komi. The English term "compensation points" or simply "compensation" is often used as a translation for komi, which is short for komidashi.[5]
A typical value for komi is in the region of 6 points, but numerous different values have been used in practice - see below for details. To prevent a drawn game in the case of jigo, the komi is commonly set to a fractional value such as 5.5 (which is a succinct way of expressing "White gets 5 points compensation and wins in the case of jigo").
With the notable exception of the Oteai, almost all tournaments nowadays, both amateur and professional, use komi. But this has not always been so. In fact, komi was rarely used in professional tournaments before 1937, and its gradual introduction into professional play was not without controversy.
The usual komi in Japan was for some time 4.5 points (specified as 4 points with White winning jigo)[4], although even lower values were commonly used early on. In 1955 the Oza became the first tournament to adopt 5.5. Today the standard komi in Japan is 5.5 points, although the Nihon Ki-in decided to change to 6.5 in September 2002.[1] Korea also used to use 5.5, but is already in the process of switching to 6.5.[2] The usual komi in China was formerly 5.5, but 7.5 is now standard.[3] The Ing rules also have a komi of 7.5, specified as 8 points with Black winning jigo. Western countries often follow Japanese practice in using a komi of 5.5 points, but tournaments with komi set at 6 or 6.5 are not uncommon. The New Zealand rules specify a komi of 7. John Fairbairn has written on the History of Komi.
Because of the difficulty of determining a fair komi, a few amateur tournaments have adopted a system whereby players arrive at the komi through some form of bidding (Auction Komi).
In theory, the correct komi for a given ruleset is a well-defined concept: it is the number of points by which Black would win given perfect play by both sides. Unless the ruleset allows fractional winning margins (which none of the common ones do), this is necessarily a whole number. Due to the absence of perfect players this number cannot be determined with certainty, but it is possible to make a reasonable guess at it, at least for some rulesets.
When area scoring is used (as in Chinese, Ing, AGA and New Zealand rules), the winning margin without komi is always odd, unless there are an odd number of points in seki. Since seki is fairly rare, and since a komi of 5.5 points has proven insufficient in professional play, and since a komi of 9 is generally considered far too much, it seems likely that the correct komi is 7.
When territory scoring is used (as in Japanese and Korean rules), the score is usually either the same as with area scoring, or one point better for White. This suggests that the correct komi under territory scoring rules is either 6 or 7. (Statistical evidence from professional games suggests 7.)
This is faulty reasoning. There needs to be made a distinction here between perfect komi as defined three paragraphs above and fair komi, which can be defined as that komi that gives a person against an evenly matched opponent a winning percentage that is as close to 50 percent as possible (treating a draw as half a win and half a loss). Perfect komi stays constant, but as insights change over time, fair komi can change with them, possibly even becoming fractional despite the used ruleset if the statistics can justify it.
The DragonGoServer offers a "proper komi feature" with fine-tuned komi intervals (..., 1.5, 2.0, 2.5, ...) to balance even minor rating differences to a 50:50 chance for both players.
BQM 67: How to adjust komi to board size?
See Handicap for smaller board sizes.
illich: I did a little research using gobase.org.
I selected games on 19x19 with 5.5 komi. The results are:
Total: 12607 decided games
Black wins: 6701 games (53.15%)
White wins: 5906 games (46.84%)
And:
Black wins by 0.5: 369 games (2.92%)
So when you move games B+0.5 to W+0.5, it will be very close: 6332:6275. This means that komi of 6.5 is fair.
There is one brief analysis of komi and winning percentages at http://homepage.ntlworld.com/daniel.gilder/komistats.html and another at [DougsGoBlog#toc2].
The problem with most statistical komi analyses is that pros play to win only. The player who is behind will try to introduce complexities, while his opponent may be willing to play suboptimally in order to reduce complexities, so long as he gives up fewer points than his lead. This means completed games tend to gravitate toward small margins.
For this reason, the only reliable statistic is whether more games are won by W (or B) for a given komi. To get solid evidence of the perfect komi, we need good statistics for an upper bound. I have heard that more pro games are won by B in ING rules which use (effectively) 7.5 . This suggests the perfect komi in chinese scoring is at least 9. Since this is a scary amount of points to give W for the privilege of moving first, I would like to see much better statistics.
Searching GoBase at komi 8 gives 172 for B, 138 for W. Searching at komi 7.5 gives 483 for B, 566 for W. I did not filter for tournament games only, so this may include games where the stronger player is W.
In handicap games a komi of half a point is often given to White in order to avoid a drawn game.
Komi can also be used in handicap games to compensate for differences in strength that exceed the traditional maximum handicap of 9 stones. Such a komi, given to Black rather than to White, is called "reverse komi" (gyaku komi in Japanese).
Komi can also be used to 'fine tune' a handicap. This is especially useful on small board Go, such as on a 9x9 board, where a single handicap stone compensates for a much greater difference in strength than is the case on a 19x19 board.
[1] Nihon Ki-in looked at about 15,000 tournament games from 1996 to 2001 and found that Black won 51.86 % of all games, a margin of nearly 4 percent over White. The directors voted to change to 6.5 komi and negotiate with the Kansai Ki-in and tournament sponsors.
[2] The first significant professional tournament to adopt 6.5 komi seems to have been the 3rd LG Cup in 1998. This was an international tournament, but Korean-sponsored. Some Korean tournaments are still using 5.5 komi in 2002.
[3] Under Chinese rules there is very little practical difference between 5.5 and 6.5 komi, hence the jump directly to 7.5. Note also that in China it's usual to talk of 2.75 or 3.75 zi (子, meaning stone), rather than 5.5 or 7.5 komi.
[4] I was in Japan during the transition to 5.5 point komi. Then most pro games used a 4.5 point komi, but some used a 5 point komi with White winning jigo. I am unaware of any Japanese pro games with a 4 point komi with White winning jigo. -- Bill
[5]
Bill: Really? I thought that komidashi meant komi given, or giving komi.
See also:
For an alternative to komi, see Pie Rule.